This invention relates to the mechanical harvesting of trellis-supported grapevines.
A typical vineyard consists of a series of rows of stakes which in turn support an arrangement of horizontal trellis wires running along each row, forming a trellis system to provide support for the individual grape vine growth and the attendant fruit thereon. A generally vertical vine trunk will be typically located at each stake with vine growth trained longitudinally on and along the wire structure. The layout of the modern vineyard is relatively standarized with about 500 vines per acre.
There are two types of training which predominate. One, cordon training, requires that the longitudinal vine growth be fastened to the wire securely where it will remain for many years. The fruit is borne on wood which was originally grown the previous year, so with this type training the year's growth is cut back almost to the cane trained on the wire, i.e., the cordon. These short, carefully selected "spurs" will produce a crop the following year and must be replaced each year from growth along the cordon. The other, cane training, also uses a vine (cane) fastened to the wire as in cordon training but the canes used are replaced each year from new growth out of the head of the vine, i.e., the area immediately above the trunk where the growth branches out. In either case the wood which actually bears fruit is replaced each year by wood grown the previous year. If this new growth is damaged or removed during harvesting, then that wood will not be available for production the following year and the yield from that vine will decrease substantially. Additionally, damage to such growth will expose the plant to serious injury from fungus and insects.
The major fruit bearing area will begin at the base of the fruiting wood next to the trellis wire and extend outward. The actual fruit production will vary quite considerably depending on the specific variety, the geographical location of the field and the age of the vine. This production will vary from a few pounds per vine for a young low yielding variety to 100-120 pounds per vine for an older, heavier bearing variety. The pruning of the vine controls to a large extent the actual location of the fruiting area. It is generally desired not to have the fruit growing in tight clusters in a congested area since the fruit cannot be covered effectively then by the fungicides and insecticides which are an essential part of modern viticulture. Although fruit production in the vicinity of the head of the trunk is minimized by pruning practices, there will still be 10-15% of the total production in those areas. The trunk area of the vine is quite rigid, the cordon area is somewhat less rigid and the fruiting wood is more and more flexible with increasing distance from the cordon and trellis wire. The fruiting area of the vine is quite extensive on the heavier yielding varieties and may extend two feet or more outwardly from the trellis wire. The large amount of fruit produced also results in the extensive vine and leaf growth which is essential to provide the nutrients for fruit production.
All successful harvesting mechanism to date have been based on some means of agitating or shaking the vines and fruit to cause detachment of the fruit. The ease of removal the fruit varies considerably. Some varieties are easily removed, some have a very tenacious connection to the stem. Some varieties have a tough, hard-to-damage berry and some have a very delicate, easily damaged berry. The actual mode of fruit removal on present mechanisms also varies. Some machines directly contact the fruit to cause detachment of the berries and bunches. Other machines use a shaking action which attempts to remove the fruit by causing relative motion between the fruit and the vine and by using the inertia of the fruit to break it loose.
The mechanism in use in the majority of grape harvesting machines today utilizes a series of striker rods which oscillate into and out of the foliage to dislodge the fruit largely by direct contact. Typically, four banks of 3-foot long, 3/4-inch diameter fiberglass rods are positioned in vertical planes with the rods being oscillated horizontally about their forward ends so that the free ends of the rods move towards and away from the vine growth to strike the grapes off of the vines. Since actual contact is the major mode of removal the entire vine structure must be struck repeatedly until the rods have penetrated the foliage completely enough to remove all of the fruit.
The striker rod system of harvesting has a serious disadvantage in that it requires a high rate of approximately 400-450 cycles per minute of striker rod operation to remove the fruit from the vine growth in the vicinity of the head of the trunk. This area of fruit growth is very congested with permanent vine arms which protect the fruit. Also, in vineyards where a trellis stake is placed at each vine trunk, the stake also congests this area, making it difficult to remove the fruit with striker rods and thus requiring an excessive rate of operation to beat the fruit off. This high rate of operation results in significant breakage of canes and removal and shredding of leaves along with the fruit. Some of the white varieties such as french colombard and chenin blanc (which are represented by large plantings) experience an objectional deterioration in quality. Even with special handling the presence of the shredded leaves mixed with the fruit can cause the formation of aldehydes which gives the wine an "off" flavor. Additionally, the damage to the vine can cause lessening of the productivity in following years and an increased susceptibility of the vine to diseases.
The area along the row between the vine trunks, however, is much easier to pick by striker rods and a lower rate of striker rod operation is required to remove the fruit because the fruit is hanging relatively free without the congestion of permanent vine arms and trellis stakes. However, it is not possible to adjust the rate of striker rod operation to pick the fruit at the exact minimum rate as the harvester is progressing rapidly down the row. As a consequence the machine operator has no choice but to have the striker rods operate at a constant speed and at the high rate needed to remove the fruit from the vicinity of the trunks. The result is that the foliage and fruit in the areas between the trunks is beaten at excessive rates, causing vine and leaf damage similar to that in the vicinity of the trunks.
There has been some work in recent years on a system for shaking the vine trunks and trellis system to remove the fruit. In particular, this system uses opposed shaker members which engage the vine trunk and/or trellis parts therebetween and shake them horizontally back and forth so that the inertia of the fruit will cause the fruit to be dislodged from the shaking vine.
The trunk shaking method has had excellent results in that much less damage is caused to the vine growth along the trellis wire and much less leaves are removed with the grapes.
However, the trunk shaking method has a considerable drawback in that the overall efficiency of harvesting is not as high as with the striker rod systems. In the vicinity of the head of the trunk and harvesting efficiency is quite high since the transfer of the shaking energy from the trunk and trellis part to that area is quite good. The energy transfer to the remoter areas of the vine growth will be less and less, depending on the resiliency of the vine growth trained along the trellis wire. Some varieties, such as zinfandel, tend to have a great deal of vine growth at the end of the permanent cordon which is sometimes 21/2 to 31/2 feet away from the head of the trunk and a heavy fruit load thereat. In order to harvest the fruit at these remote areas by the trunk-shaking system, the system must operate at high energy levels and in such manner that sufficient energy is transferred away from the trunk vicinity to the remotely located fruit.
Attempts have been made to operate the shaker type harvesters at a low ground speed so that each trunk is shaken for a longer time. This does increase the amount of fruit removal. However, this results in an uneconomically slow harvest speed. Harvest speed is very important as the fruit must be harvested at the peak of ripeness when the sugar-acid ratio is at the desired level. This peak point can last less than a week during which time the fruit must be totally harvested. Grapes have the characteristic, unlike some fruits and vegetables, that a particular variety in a specific geographical location will usually ripen at the same time over each vine and each field.
In order to harvest grapes by the trunk shaking system with a good harvesting efficiency and acceptable speed, it has been necessary to operate these systems at a high rate, typically 400-425 cycles per minute and with a relatively high shaking stroke. Unfortunately, this often causes the trunks to split where they branch off into the cordons and/or causes breakage of the trellis posts.
Further, there are several trellis-supported vine systems which are not adapted to be harvested by trunk-shaking systems. For example, in vineyards wherein the vines are trained so that there are only one-year old canes trained along the trellis wire, the canes are usually too limber to transfer sufficient shaking energy therealong to cause fruit removal. The same is true in cordon trained vineyards wherein the cordons are still young and quite flexible. In some areas with some varieties, there is a practice of leaving a lateral (referred to as a "kicker" cane) extending from the end of the cordon up to and attached to the top foliage wire of the trellis system, the kicker cane being used to secure the end of the cordon so that it will not twist and roll over as the vine grows or as the wind blows and puts a bending force on the upwardly growing foliage. The kicker cane also results in more fruiting buds on the vine and thus increase the crop. However, because the kicker cane is quite limber and carries fruit at a location away from the trellis wire, such fruit cannot be effectively harvested by a trunk-shaking system.
As is apparent from the foregoing, there is a need for a mechanical grape harvesting machine which is usable for any standard trellis-trained grape system, which is operable at commercially acceptable ground speeds, which has a high harvesting efficiency, which has low leaf removal and which causes minimal damage to the vine growth, trunks and trellis parts.